I always had a hard time understanding why Jack shows any measure of trust in Will after him tells to his face that he wishes he had ran away with Hannibal (twice), but I think that at, long last, during this rewatch it dawned on me the reason why.
Because you see, Jack understands the appeal of this relationship for Hannibal. I think he's very insightful when he talks with Pazzi about it, about how Will is able to understand and accept Hannibal.
But I don't think that Jack believes that Will's desire to be with Hannibal is genuine. I think he believes that this is a byproduct of Will's empathy being off the charts, and that he is confusing Hannibal's desires with his own.
He tells him as much, during Tome-Wan:
And when he's talking with Pazzi, he also tells him that he "broke" Will's imagination.
And in Dolce, when Will tells him part of him will always wants to be with Hannibal, he just tells him to cut it out.
I think this is why during the Red Dragon arc Jack still looks for Will's help. While I think by that time neither one of them is interested in their friendship anymore and their relationship is purely professional (even a hostile professional relationship at times), I think Jack still believes he can trust Will and use Will's imagination with moderation, since Hannibal is behind bars now, and because Will has a family now - therefore a more stable, grounded life.
Maybe he thinks Will finally shook off Hannibal's influence enough to move on with his life, and when Hannibal tries to have Will's family killed I think he believes he can trust that Will will finally be willing to permanently remove Hannibal from his life by killing him.
It is, of course, a very risky gamble. A gamble he loses, and one he pays for, dearly.
As a member of the audience, it may look for us like Jack is being too trusting and too naive, but I think it's fair to remember that Will has kept a LOT from him. There's so much Jack doesn't know about his relationship with Hannibal.
Jack likely doesn't know that Will willingly (even gleefully) partook in cannibalism with Randall Tier's organs in order to fool Hannibal that he had killed Freddie Lounds. He never heard Will telling Hannibal how much he enjoyed killing Hobbs and Tier, never saw their conversations by the fire. He never saw the way Will speaks with Chiyoh and what he does to her and the prisioner, and he never saw the way he threatens Bedelia.
He never saw the look on Will's face when Hannibal snapped Mason Verger's neck.
He doesn't know that Will was worried if Hannibal could ever be happy while in prison. He didn't see the torn expression in his face when Hannibal didn't give him a fully positive answer.
Most of all, he doesn't know that, after the events of Mizumono, when Will fantasizes about a better world, he thinks about a world where he had chosen Hannibal sooner and had chose to go along and murder Jack with him.
Jack's perception of Will and Hannibal's relationship is distorted by how little he knows about how things really are beetween these two.
And I think Jack doesn't want to believe in Will has such a darker side on his own, because Jack is not the kind of guy who likes to be this wrong. During Will's trial, he struggles with the idea of having been that wrong about him, that his instincts where so wrong. And since the first season Jack has a habit of choosing to believe in the version of events that will better suit him, not matter how likely or unlikely they are.
The idea that after how much he stood by him, that how much he bled and suffered by plotting with Will at the end of season two, that Will has the capacity for so much violence and darkness is something he doesn't want to accept. Easier to see Will as someone who was broken and damaged, maybe beyond repair during the epic struggles Jack has with Hannibal in the course of the seasons than to believe this.
Alana tried to warn him as early as the end of season two that he didn't know any of those men, and if he forced the issue, he was bound to lose.
I think that, during a potential season four, Jack would only realize the colossal weight of his mistake in trusting Will to handle the plan with Hannibal's "fake" escape only when they had proof that Hannibal was still alive and Will had joined then, or when Bedelia showed up sans one leg.
But still, even with the ending that we got in the third season, Jack's decision to close his eyes to Will's darkness and genuine feelings for Hannibal ends up making Jack lose very, very badly.


















